GameDevMarket.net
Great quality (but budget priced) 2D and 3D artwork you can use in your own games.
KoboldTouch
An easier/better way to use Cocos2D for 2D game development.
OGT Level Manager
Lock and unlock levels easily with OGT Level Manager for Corona SDK.
Super Sprite Bundle
Royalty-free graphics for 2D games - animated characters, tile sets, etc.
Pathfinding Tutorial
Use Corona SDK and the free Jumper library to do A* pathfinding in your games - over 60 minutes of video + sample code!